In order to comply with regulatory requirements in relation to emissions from combustion engines, it is known to recirculate exhaust fluids in order to provide a further opportunity for combustion in the engine and also to provide exhaust fluid treatment apparatus to receive and treat exhaust fluid emitted by the combustion engine.
A combustion engine, such as a diesel engine, may involve injection of fuel, such as diesel fuel, into one or more cylinders of the engine for combustion. In addition to injection of fuel for combustion, fuel may be injected into one or more of the cylinders as a post combustion event with the intention that the fuel passes out of the one or more cylinders without oxidising. Such a technique may be useful when the combustion engine is used with an exhaust fluid treatment apparatus. This may allow for unburnt fuel to be delivered to the exhaust fluid treatment apparatus. Unburnt fuel may oxidise in the exhaust fluid treatment apparatus which may be useful when there is a desire to increase the temperature in the exhaust fluid treatment apparatus or when there is a desire to burn off, for example, unburnt carbon in the form of soot which may collect in a diesel particulate filter of the exhaust fluid treatment apparatus.
It may be desirable to control the engine in order to manage, in combination, both the supply of fuel intended not to combust in the cylinders and exhaust fluid recirculation. Such engine management may be intended to maximise any or all of engine efficiency, emission reduction and system reliability.
Against this background there is provided a method of controlling operation of an engine.